1. Field of the Invention
The present invention relates to a semiconductor device and a liquid crystal display device. In particular, the present invention relates to a semiconductor device and a liquid crystal display device in which liquid crystal molecules are controlled by generating an electric field having a component parallel to a substrate.
2. Description of the Related Art
One of technical development strategies of a liquid crystal display device is to widen a viewing angle. As a technique for realizing a wide viewing angle, a method is used in which a gray scale is controlled by generating an electric field parallel (i.e., in a lateral direction) to a substrate to move liquid crystal molecules in a plane parallel to the substrate.
Examples of such a method include an IPS (In-Plane Switching) mode and an FFS (Fringe-Field Switching) mode.
In an IPS mode liquid crystal display device, two comb-shaped electrodes (also referred to as comb-teeth electrodes or comb electrodes) are provided over one of a pair of substrates. Liquid crystal molecules are moved within a plane parallel to the substrate by a horizontal electric field generated by potential difference between these electrodes (one of the comb-shaped electrodes is a pixel electrode and the other thereof is a common electrode).
In an FFS mode liquid crystal display device, a second electrode (e.g., a pixel electrode in which voltage for each pixel is controlled) having an opening is provided below a liquid crystal, and a first electrode (e.g., a common electrode in which common voltage is applied to all pixel) is provided below the opening in some cases. An electric field is applied between the pixel electrode and the common electrode to control the liquid crystal. An electric field in a parallel direction is applied to the liquid crystal, so that liquid crystal molecules can be controlled using the electric field. That is, liquid crystal molecules aligned parallel to a substrate (so-called homogeneous alignment) can be controlled in a direction parallel to the substrate, so that a viewing angle is widened.
In conventional semiconductor device and liquid crystal display device which control liquid crystal molecules, a pixel electrode or a common electrode has been formed of a light-transmitting conductive film, for example, indium tin oxide (ITO) (see Patent Document 1: Japanese Patent No. 3742836).